Apparatus for solvent-isostatic pressing



April 13, 1965 P. B. ARCHIBALD 3,177,553

APPARATUS FOR SOLVENT-ISOSTATIC PRESSING Original Filed Dec. 30, 1960 E j s! 3; 32

l I i f 3l` E l I u30 i t 49 @44. E 5,

INVENTOR.

PAUL BARcH/BALU BY Ma-fm ATTORNEY United States PatentOFice 3,177,553 Patented Apr. 13, 1965 3,177,553 APPARATUS FOR SLVENT-ISSTATEC PRESSING Paul ll. Archibald, Pleasanton, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Original application Dec. 30, 1969, Ser. No. 7%940, now Patent No. 3,054,147, dated Sept. 18, 1962. Divided and this application Nov. 13, 1961, Ser. No. 156,554 2 Claims. (Cl. 25-45') This is a division of my application Serial No. 79,940, filed December 30, 1960, which issued as Patent No. 3,054,147, granted September 18, 1962.

This invention relates to the production of compacted ybodies and, more particularly, to an apparatus for the production of large compacted bodies by a low pressure pressing operation.

Ram-and-die pressing operations are usually limited to the production of relatively small objects, since the dies required for large objects are prohibitively expensive. In order to produce large compacted bodies, isostatic pressing is usually resorted to. In the practice of conventional isostatic pressing, the material to be compacted is placed in powder form inside a strong iiexible bag. The bag is to 50,000 pounds per square inch are commonly used in industrial isostatic pressing. High pressure operation requires heavy thick-walled apparatus and conventional iso- Lstatic presses are generally large expensive pieces of equipment.

The present invention provides apparatus for conducting sostatic pressing operations at pressures substantially below those required by the prior art. In using the apparatus of the invention, a limited amount of suitable solvent is added to the powder which is to be compacted isostatically. The solubility of the powder granules in the solvent is highest at the points of greatest mechanical stress, i.e., the points of contact between adjacent granules. Therefore, the solvent effects a localized solution vat these contact points. When this saturated solvent iiows into the void spaces in the powder, wherein the mechanif cal stress is less than that at the contact points, the dissolved material is redeposited in the void spaces. rlhe resulting decrease in total void space enables the pressing operation to be carried out at a much lower pressure than would be possible in the absence of any solvent. Apressure of 2,000 p.s.i. is typical in the practice of the invention; ,this corresponds to 5-10% of the pressure commonly used in conventional isostatic pressing. As a result of the low pressures employed, the present apparatus makes possible the use of relatively light and inexpensiev pressing equipment. f Accordingly, it is the main object of the invention to provide novel apparatus for performing solvent-isostatic pressing operations.

The invention will be described with reference to the accompanying drawings, of which:

, FIGURE l is a cutaway view of a preferred embodiment of a novel apparatus for conducting solvent-isostatic pressing;

FIGURE 2 is a cross sectional View of an apparatus for the production of tubular compacted bodies by solvent-isostatic pressing;

FIGURE 3 is an enlarged view of plug assembly 38 shown in FIGURE 2; and

FIGURE 4 is an enlarged view of pressure coupling 44 shown in FIGURE 2.

Referring now to FIGURE l, there is shown a flexible bag 11, which is securely clamped at its open end to a rigid container 12 by means of an annular clamp 13. A finely perforated plate 14, of a diameter equal to that of container 12, is disposed across the open end of the container, and is secured to the walls thereof. Within eXible bag 11 are disposed a granular charge material 16 and a solvent 17 in mutual contact. The assembly of flexible bag 11 and the contained solvent-granular ymaterial charge, and rigid container 12 is immersed in a fluid medium 13 contained within a pressure vessel 19'. A tightly fitting threaded plug 21 and a pressure gasket 22 seal the opening of vessel 19, and a fluid conduit 23 communicates with the interior thereof. Fluid medium 18 is supplied to the pressure vessel from a fluid reservoir 24 connected in series with a high pressure pump 26. A pressure regulator 27 is disposed between pump 26 and vessel 19, so that a constant pressure can be maintained in the vessels interior. Support ring 28 serves to position the bag-container assembly within the pressure vessel. Y

In the operation of the apparatus illustrated in FIG- URE 1, a measured volume of solvent 17 is poured into Flexible bag 11, and the granular charge material 16 is added thereto. The bag is clamped to rigid container 12, and the assembly is inverted and positioned within vessel 19 by means of support ring 29. Pump 26 is switched on, and hydraulic fluid from reservoir 24 is forced under pressure into vessel 19. When the pressure in vessel 19 has reached the desired value, regulator 27 is adjusted to maintain this pressure. The increased fluid pressure inside vessel 19 constricts tiexible bag 11, thereby causing solvent 1'7 to percolate through the charge material 16, dissolving the granules at their contact points and redepositing the dissolved material in the void spaces of the powder. As compaction proceeds, the solvent is ultimately squeezed completely through and thereafter from the charge material and subsequently flows through perforated plate 14 into the closed end of rigid container 12. Granules of the charge material are prevented from falling into container 12 by the filtering action of plate 14. After the charge material has been under pressure for the required length of time, the pressure in vessel 19 is released and the compacted object is recovered from bag 11.

The main advantage of the solvent-isostatic pressing apparatus over conventional isostatic pressing equipment is that the presence of a solvent in the material to be compacted enables the pressing operation to be performed at a much lower pressure than would be possible in the absence of any solvent. The solubility of the material to be compacted is greatest at the points of contact between adjacent granules when the granules are under mechanical pressure. Therefore, when pressure is applied to the charge material, the solvent effects a localized solution at the contact points between adjacent granules, and redeposits the dissolved material in the regions of least mechanical stress, i.e., the void spaces between the individual particles. As the applied pressure is increased, the solubility of the granules at their contact points correspondingly increases, and the available voidv space becomes filled with redeposited material. It is apparent resulting compact that is virtually impossible to achieve Y material. v

in 'conventional non-solventisostatic pressing operations; y v l Y v l, Typical pressing times at Vroom-temperature areon the order ofy -50 hours, however, in `many ceases, the time requiredto compact the chargelcan bel substantially re- Yduced bycarrying outl the pressingoperation at elevated temperature. Y .Thisv can be done bylheating the hydraulic Yfluid in the reservoir, Yorby disposing animmersion-type heater-fin the pressure vessel. The bag-container assem-l bly shown in'EIGURE l is 'aclosed system, so that the pressingoperati'on can be conducted at temperaturesjwell above theatmos'pheric boiling point ofthe solvent.

TheY relative proportion of Vsolvent tocharge materialY is critical to the successful operation` of vthe pressing apparatus. If'insufficient solvent isr added to the? charge material, ',the'solv'ent will'not distribute uniformly vamong Y Y y' Y 3,177,553

a minimum of void space when pressureis applied; It has vbeen found that the optirnummean particle diameter for solvent-isostatic pressing ylies between six and ten microns'l Powders having mean particle diameters sub stantiallygreater than ten microns require pressing times whichimayjbetoolong tofbe practicable.' Y j f Althoughthe' main advantage ,of solvent-isostatic pressing irsthat if can be performed at ypressures substantially below those required by conventionalv isostatic pressing, it is sometimes .advantageous'lvtoemploy. a high pressure press in order to reduce the/'pressing time. In such cases, the addition'of solyent'before pressing'. ywillstill, produce a denser and more homogeneous compact vthan would be l obtained by non-'solvent pressing atthe same pressure.

The apparatus ofthe invention ycan rbe used tofadvanp tage for the pressing of many different materials. V `The only"restrictions' o'n the nature of the charge material are that it ,canV be obtained las a crystalline powder preferably 'Y vhaving a mean particle diameter ofsix to tenl microns,

fand thatfa sint-ablev solvent' is availableforfthe powder.

Materials which have'been successfully pressed include;

lIt has been foundthatfthe optimum solvent concentration Y lies in thefrange of -15% by weight of the dry charge The only restriction on` the chemical composition of the solvent to be used with the apparatus of the linven-v tion is that there be no chemical reaction between theYK solvent and ,the charge material. Satisfactory compacts have been obtainedfusing water, acetone, ethanol, meth* anol, dio'xane, and various mixtures Ythereof as solvents.

If the material to be compacted is very soluble` in they particular solvent selected, thenV substantial'amounts of the charge willA dissolve in thesolvent and, unlessrecovered therefrom, will be lost.y Howeventhi's loss. of charge material canrbe Iminimized by pre-'saturating the solvent with the chargematerial, and using this saturated solventin the pressing operation.' Since Vthe solventis already saturatedv with `the charge material; a. dynamic i ,equilibrium fbetween'solvent andsoluteY is set up, the

V'crystalline organic compounds,v e.g.trinitrobenzene, inorgarlic ,sa-lts -such as ammonium nitrate, and mixtures thereofwith powdered'metals, specifically, powdered alu- TheV Ysolvent-is'ostatic. pressing apparatus can be used for'the productionof variously shaped compacts by sirnply disposing a suitably shaped mandrel within the ilexiblebag,an l disposing the solvent and charge mateirial around themandrel'. Aluminum mandrels have .'been'used toA press hol-low hemispheres; cylindrical shells,

andv other'simple geometrical shapes.r A novel apparatus lforftlie productionbf tubular compacts isillustrated in FIGURE V2V, wherein there is shown atubulafr housing'29 enclosing? a lsolvent-moistenedV charge material 31. An "inflatable el'as'tomerictube 32 is axially disposed within `lousirigf29,v and is surrounded along its length 'by 'charge material' 31. The ina'ted position of tube 32 is: indicated l bythe dottedy outline 30,'1' I erforated'plates 33 and 34v are 'rate offsolution into ,the solventbeing equalv to, the rateV of deposition 'outof the solvent. In thismanner,the;useV

of asaturated solvent will. minimize materialV losses in ,the 'Y solvent, while still effectively decreasing the voidspace inA the, iinished' compact. L

In many cases, mixtures of 4organic and inorganic. mate;-

rials can be successfully solvent-isostatically pressed, pro,- l

'vided that. arsolvent can lbek found in whichY either'the organic orvthe inorganic component is'appreciably soluble. Forexample, ammonium nitrate is soluble in `acel tone to vthe extent of 17 grams per 100n'1illilitersofV acetone. This solubility aifords a vmeans whereby ammo.'

nium nitrate canbepre'ssed in admixture withany organic Y orinorganicmaterial. ln the solvent-isostatic pressing ofV mixtures,as `well as in the pressing of single compounds, the loss of Y charge material in the solventcan bek vminimizedv by saturating the vsolvent beforeuse'i'n the `pressing operation. For` thepressing'of mixtures, the 'solventi is rst saturated'separately with earch of the pure ycomponents comprising themixture;` *This* insures'vthat the sol'- vent will not dissolve any `ofthe' components selectivelyy -during thepressing operation.- Y i 1 Vdisposedvvithin housing 29 so as to divide the interior of fthe housing `into three chambers; anuppersolvent recov- -erychanrber 3 6,1a,` middle chamber containing the solventmoistened charge materiaLand a lower solvent recoveiy chamber'l iA supportingsleeve 35 .is fixed to theA upper surface of v'plate 33, ,and; tube 32 ,passes therethrough. -Lowler plate34lrests on. annular 'shoulder Vformed into -the yinterior 'wall ofihousirgf29j,andupperplate 33 rests -directly'on the; chargernaterial 31.,y The' lower end -of :tube32: issecured toV plate34-by means offay pressure plug V'assembly-38. Solvent recovery pipes 3,9*ar1d41 communicate Ywithrjjcharnbersf 36 and '37 respectively.A A anged cover 42 -isY boltedI toj .the open, end; of housingv 29 by means" offcircumferentially disposed boltsA 43. The .lowerxsurfacefof coveri42 bears-'against the upper end of .sleeve 3,5.- "Inatable, tube,32v passesthrough cover 42 and is secured-theretoV by pressure coupling 44; The

i @coupling also,serves to connect tube? 32 toV an external source-o hydraulicrluid` under pressure (not shown). Tube 32 'isi preferably fabricatedffrom a synthetic It willibe apparent from` the foregoingldiscussion that f 'the application of pressure to the charge mixture causes the individual granules therein to consolidate themselves into a closely packed structure.` VThe'clos'estjpackin'gof v a particulate mass is obtained. when the diameters' ofthe t particles therein are'- distributed accordingtoaGaussian frequency` distribution, Le., where there'are many diierentparticlerdiameters symmetrically distributed about'a lmean diameter. For'purposes lof the present invention,r ysuch a particle distributionzcan be obtained through ball milling or grinding the `particles in a mortar. This procedure insures that the particles will pack togetherV with jelastometen-eg;neoprene. 1 n 1 AV detailedy viewof plug,v assembly V38 is shownin FIG- `-URE 3*.A threadedmconicalfplug: 46 is'screwed into a correspondingly threadedboss 14']` lwhich is secured to the ',lowersurfaceoff };91ate-.34.` L'Iheconical surface ofeplug 46 bears against tube 32'and`deforrns the 4tube into serrations/45 formed fin boss`47 Tube 32 ,is therebytightly A detailed'view of pressure .coupling l-44fis ,Y shown ,is FIGURE 4.-n Ananemaliyfthreadevd emanating-Y 4s,

having a conical boreyisaixed to the vouter surface of Acover 42;v. -A- male fitting' 45?,.v-harvinganV externalptaper corresponding-to lthefr'cpzonical :bore oftting y{18,*bears againstinatable ,tubeY 32, and'deforms the tubevinto serrations 5 0 eformedinto thebore of fittingy 48; A coupling yits lower end. A Asolvent-meistened charge material 31 is packed into the housing surrounding tube 32, and the tube is threaded through plate 33 and attached sleeve 35 which are placed on the upper surface of the charge material. Cover 42 is then bolted on and tightened until the lower surface of the cover exerts a slight pressure against the upper end of sleeve 35. Hydraulic iiuid under pressure from the external reservoir is admitted to tube 32 via coupling 44. Tube 32 iniates to the position indicated by the dotted outline in FIGURE 2 and, in so doing, compresses the charge material against the interior wall or" housing 29. Solvent is squeezed out of the charge material and ows through plates 33 and 44 into the solvent recovery chambers 36 and 37. Solvent is recovered from the system through pipes 39 and 41..` After all the solvent has been squeezed out of the charge material, and the hydraulic pressure yhas been released, the resulting'tubular compact is recovered.

The apparatus shown in FIGURE 2 is` especially suited to the production of compacted bodies having symmetry about about a central axis, e.g., rocket propellant grains. The interior wall of housing 22 can be suitably machined yso as to shape the outer surface of the compacted body to any desired configuration. For example, if a cruciform conguration is desired, four longitudinal ribs can be xed to the interior wall of the housing.

Although several embodiments and examples of the invention have been described herein, these are intended to be merely illustrative, and various modications can be made therein without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

1. An apparatus for producing compacted bodies from a powdered material comprising:

(a) a deformable container adapted to contain said powdered material,

(b) a rigid container removably connected to said ydeformable container,

(c) a perforated partition disposed between the respective interiors of said rigid container and said deformable container,

(d) a solvent in which said powdered material is at least partially soluble disposed within said deformable container in contact with said powdered material, and

(e) means for isostatically compressing said deformable container.

2. The apparatus according to claim 1, wherein said solvent is selected from the group of oxygenated organic solvents consisting of acetone, ethanol, methanol, dioxane, and mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 342,178 5/86 Carmichael 162-402 1,081,618 12/13 Madden 18--59.4 1,226,470 5/17 Coolidge 18-59.5 X 2,173,593 9/39 Phelps 25--45 2,336,428 12/43 Watson 1GO-211 2,528,643 11/50 Dubbs. 2,542,874 2/ 51 Locatelli 2545 2,648,125 8/53 McKenna et al 18-59.4 2,685,189l 8/54 Watson 100-211 3,015,855 1/62 Merkel 18-59.5 X 3,034,191 5/62 Schaefer et al 25-45 FOREIGN PATENTS 465,922 5 37 Great Britain. 279,632 11/3 0 Italy.

WILLIAM J. STEPHENSON, Primary Examiner.

MICHAEL V. BRINDISI, ROBERT F. WHITE,

NEDWIN BERGER, Examiners. 

1. AN APPARATUS FOR LPRODUCING COMPACTED BODIES FROM A POWDERED MATERIAL COMPRISING: (A) A DEFORMABLE CONTAINER ADAPTED TO CONTAIN SAID POWDERED MATERIAL, (B) A RIGID CONTAINER REMOVABLY CONNECTED TO SAID DEFORMABLE CONTAINER, (C) A PERFORATED PARTITION DISPOSED BETWEEN THE RESPECTIVE INTERIORS OF SAID RIGID CONTAILNER AND SAID DEFORMABLE CONTAINER, (D) A SOLVENT IN WHICH SAID POWDERED MATERIAL IS AT LEAST PARTIALLY SOLUBLE DISPOSED WITHIN SAID DEFORMABLE CONTAINER IN CONTACT WITH SAID POWDERED MATERIAL, AND (E) MEANS FOR ISOSTATICALLY COMPRESSING SAID DEFORMABLE CONTAINER. 